1. Field of the Invention
The present invention relates to a solid-state imaging apparatus and an imaging system which uses the solid-state imaging apparatus.
2. Description of the Related Art
Recently, a solid-state imaging apparatus corresponding to an image of 10,000,000 pixels has been used for a digital still camera. This is a result of pursuing an image quality which can be usually obtained by a silver salt camera (i.e., a film-based camera), and the solid-state imaging apparatus of this type is mainly used exclusively for a still image. On the other hand, it should be noted that the number of pixels necessary to obtain a moving image of which the quality substantially corresponds to that of a full high definition television system is 2,000,000 pixels or so.
If the solid-state imaging apparatus corresponding to the image of 10,000,000 pixels is used in regard to a moving image, a reading speed as much as about five times the reading speed in a case where a solid-state imaging apparatus corresponding to an image of 2,000,000 pixels is used to obtain the moving image is necessary. In this case, following problems occurred. That is, since electric power consumption highly increases, noises caused by such increase of the electric power consumption has an adverse affect on an image quality. In addition, since a memory capacity to be used for an image processing increases, manufacturing costs of the apparatus increase.
Thus, in order to increase the reading speed and reduce the electric power consumption, there is a method of adding and reading signal charges. More specifically, Japanese Patent Application Laid-Open No. 2006-073733 discloses a solid-state imaging apparatus which can perform same color addition in a unit pixel group in regard to each color by using the unit pixel group constituted by a common amplifier having four rows and one column.
However, in such an addition method as described in Japanese Patent Application Laid-Open No. 2006-073733, the addition in the unit pixel group can be performed only in the vertical direction. That is, in this method, the addition of the pixels adjacent in an oblique direction cannot be performed. That is, if the addition of the adjacent pixels is performed only in the vertical direction, image information of each color after the addition was performed comes not to have spatially equal intervals. Thus, there is a problem that resolution deteriorates. For this reason, it is required to add pixels signals respectively indicating the pixels arranged in the oblique direction. In this connection, it is necessary to provide an addition unit to add the pixels adjacent in the oblique direction. More specifically, it is necessary to add a line memory or the like. At this time, a process of writing the signals of the pixels adjacent in the oblique direction in the line memory respectively and then performing the addition to the written signals has to be performed. This process prevents from improving a frame rate.
The present invention aims to solve the conventional problems as described above. Moreover, the present invention aims to provide a solid-state imaging apparatus which can photograph a high-definition image and also can photograph at high quality a moving image of which the resolution is lower than that of the high-definition image, and to provide an imaging system which uses the solid-state imaging apparatus.